Feeds

Saturn's Phoebe 'most like Pluto'

Origins of rocky moon revealed

  • alert
  • submit to reddit

Intelligent flash storage arrays

The latest data sent back from the Cassini spacecraft, along with previously-gathered results, have confirmed that the mysterious moon, Phoebe, is a remnant from the early days of our solar system.

Astronomers suspected Phoebe was a captured moon, and now they have the proof: composition data sent back by Cassini shows that of all the objects we have studied in the solar system, Phoebe is most similar to Pluto. She matches the composition expected of the objects in the Kuiper Belt, an icy region beyond Neptune, and thought to be the place most comets come from. Indeed, some speculate that Pluto itself is a Kuiper Belt object, not a planet at all.

Torrence Johnson, on the Cassini science team at the Jet Propulsion Laboratory, said: "This is pretty good evidence that Phoebe was put together in the outer parts of the solar system."

So, at more than four billion years old, Phoebe is a battered, but otherwise perfectly-preserved example of the protoplanetary building blocks that eventually combined to form the planets.

Speaking to Nature, Johnson explains that the outer solar system would have been chock-full of icy planetesimals like Phoebe. Many of these bodies collected together to form the cores of the gas giants. Most of the others were swept into the outer solar system by the gravitational effects of these new, huge, planets. Phoebe remained behind, dragged into her orbit of Saturn as the planet was swallowing the streams of gas that make up its atmosphere.

Phoebe: mostly round Despite having taken a heavy battering over the last four billion years, Phoebe is still mostly round with an average diameter of 214 kilometres. The spherical shape is broken up by one especially large crater whose walls are 16 kilometres high.

The details of Phoebe's radius, combined with its orbit, reveal the body's composition. It is approximately 50 per cent rock - very like Pluto - and strikingly different from Saturn's other moons, which are around 35 per cent rock.

As for the rest of the moon, the data shows frozen carbon dioxide, water ice, hydrocarbons and iron minerals all present on the surface. As well as proving that Phoebe is no asteroid, this shows that chemically at least, Phoebe is very similar to the comets, also Kuiper belt objects. ®

Related stories

Phoebe's past writ large in craters
Mysterious Phoebe: Cassini's next fly-by
Cassini images delight star gazers

Remote control for virtualized desktops

More from The Register

next story
Rosetta probot drilling DENIED: Philae has its 'LEG in the AIR'
NOT best position for scientific fulfillment
'Yes, yes... YES!' Philae lands on COMET 67P
Plucky probot aces landing on high-speed space rock - emotional scenes in Darmstadt
THERE it is! Philae comet lander FOUND in EXISTING Rosetta PICS
Crumb? Pixel? ALIEN? Better, it's a comet-catcher!
SEX BEAST SEALS may be egging each other on to ATTACK PENGUINS
Boffin: 'I think the behaviour is increasing in frequency'
HUMAN DNA 'will be FOUND ON MOON' – rocking boffin Brian Cox
Crowdfund plan to stimulate Blighty's space programme
Post-pub nosh neckfiller: The MIGHTY Scotch egg
Off to the boozer? This delicacy might help mitigate the effects
I'M SO SORRY, sobs Rosetta Brit boffin in 'sexist' sexy shirt storm
'He is just being himself' says proud mum of larger-than-life physicist
NASA launches new climate model at SC14
75 days of supercomputing later ...
prev story

Whitepapers

Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
Getting started with customer-focused identity management
Learn why identity is a fundamental requirement to digital growth, and how without it there is no way to identify and engage customers in a meaningful way.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Reducing the cost and complexity of web vulnerability management
How using vulnerability assessments to identify exploitable weaknesses and take corrective action can reduce the risk of hackers finding your site and attacking it.
Saudi Petroleum chooses Tegile storage solution
A storage solution that addresses company growth and performance for business-critical applications of caseware archive and search along with other key operational systems.